DETROIT – Vehicle fuel efficiency could be improved significantly if the U.S. would shift to higher-octane gasoline, Detroit Three powertrain chiefs tell attendees at the SAE World Congress here.

The rationale is simple: Higher-octane fuels burn more predictably and allow automakers to design engines with higher compression ratios. Higher compression ratios yield more power per combustion event and more power-dense and efficient engines.

U.S. fuel has a research octane number (RON) of about 91, while Europe has a standard of 95 RON or higher. That’s a huge difference to engine experts. If automakers could stop designing engines to avoid low-octane engine knock, engine efficiency could be improved by as much as 5%, Bob Fascetti, vice president-Powertrain Engineering at Ford tells SAE attendees.

“We have to design for regular fuel (91 RON in the U.S.). If we could get 95 RON fuel at the pump like Europe, if we could get higher compression ratios, we could get big benefits,” Fascetti says.

The idea hardly is unprecedented. The U.S. mandated European-style standards for ultra-low sulfur content in diesel fuel in 2007, resulting in dramatically improved diesel engines and emissions.

“Our (octane number) is too low,” Bob Lee, vice president and head of Engine and Electrified Propulsion Engineering at Chrysler, tells reporters on the sidelines after his presentation. Lee’s estimate for fuel-economy gains is slightly lower, but he says, “I’m giving up 2% or 3% (in fuel efficiency) just to go from 95 octane to 91.”

Higher compression ratios are beneficial in many ways, Lee says, such as improving the efficiency of Atkinson-cycle combustion strategies.

Steve Kiefer, vice president-Global Powertrain for General Motors, also says he supports a move to higher-octane gasoline.

The three powertrain chiefs have spoken about moving to higher octane at technical conferences and in Washington, where the Department of Energy is well aware of the benefits, but have not said much publicly until now.

“I can’t say we’ve actually lobbied together, but it’s a common-sense thing. If we had a single-octane fuel that was higher, then we can take advantage of that for the customer, we can implement higher compression ratios and we won’t be knock-limited on the fuel,” Fascetti says. “It’s win-win for the innovators as well as for the customers.”

Discuss this Article 6

Getting rid of the ethanol in pump gasoline would also increase fuel efficiency by at least 5% and also raises the regular octane rating of 87 up to 90. The same would be said if ethanol was removed from mid-grade (89 or 91 octane) and premium (93 octane).

But that would probably take more politics and red tape to do that rather than make an informed, smart and logical decision how to increase mpg's out of the existing fuel we have.

One thing that wasn't said in this article that should be mentioned is that with higher octane gas and higher compression engines the consumer will be spending more than today. Higher compression engines require more expensive components and higher octane gasoline is more expensive to refine. That is why I am skeptical that the market would want this.

It is my understanding that higher octane blends are lower BTU content per gallon. Ethanol blends are also lower. Why not get rid of the ethanol subsidy and allow refiner to choose. Post on pump so I can quit having my lawn equipment, power sports, and antiques damaged. Oh wait, that would need a non corrupt congress. Never mind.

But powertrain engineers are saying that if regulations and consumers want more fuel-efficienct vehicles, this is one broadbased means of improving fuel-efficiency across the board. That's how it's done in Europe.

It's garbage in, garbage out. The best diesel engines in Europe could not even be sold in the U.S. until the 2007 mandate for ultra-low-sulphur diesel forced oil companies to offer fuel that was first-world quality rather than third-world quality. The quality of U.S. fuel is holding us back in many ways. Better fuel equals more efficient engines.

Can U.S. consumers and politicians accept such a concept? We did with diesel fuel. It's not impossible.

Today the price in my town for 91 octane was 3.51 and the 87 regular is 3.19. This is R+M/2 octane not the research in the article. Estimated Research octane would be about 91 and 96. The higher octane costs 10% more. Kind of foolish to spend that much extra on fuel and get 3% mileage improvement. They only want that to meet their mileage goal. I am interested in lowest cost per mile.

10% Ethanol fuel is only about 2 or 3% lower in BTU content. On a computer controlled engine the mileage penalty is 1 to 2% MAXIMUM. There is no way it can be 10% except in poorly controlled experiments.

Back in the 50’s John Deere made spark ignited engines for JD fuel, which was pretty low octane, but made better power at the 6 to 1 compression ratio common on those engines and they also had water injection. They made less power and burned more fuel if you used gasoline.. As I understand it, JD fuel was between gas and kerosene and was really inexpensive, and the BTU content was higher than gasoline.

The entire point is reducing overall emissions/pollution. If it happens to save money, or cost very little then great. The different octane levels, ethanol levels, etc. only matter as they relate to emissions , which is predominantly regulated by MPG whether that is a true measure of emissions or not .

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